This invention relates to polymer sealant compositions.
It is known to use rubbery materials such as styrene/butadiene copolymers in sealant compositions. However, high performance sealant compositions have generally been limited to more expensive materials such as polysulfides, polymercaptans, polyurethanes, and silicones because of the difficulty of getting a good balance of properties in the less expensive rubber compositions. For instance, one of the requirements for a sealant, obviously, is a good stability to weathering. However, the unsaturation present in ordinary rubber compositions tends to make such compositions susceptible to attack by oxygen and ozone. This can be alleviated by hydrogenation but hydrogenation tends to reduce one of the beneficial aspects of such rubbery materials, the good elongation. It is known to use plasticizers to improve the flexibility of sealant compositions but some plasticizers tend to sensitize the formulation to ultraviolet light, thus making the stability worse. Also, many plasticizers are not compatible with other ingredients in the polymer or given surface tack. Polyalkenes are known for use as plasticizers but these materials tend to be incompatible with unsaturated rubbery materials.
Thus, it is apparent that heretofore the typical formulation of a sealant composition has involved a compromise between competing properties, with variations in the formulation which enhance one property tending to cause a deterioration in others. Another aspect of this situation is the desirability that the sealant adhere reasonably well to the sides of the joint or crack to which it is applied, yet after the sealant is set, it is undesirable for it to have a tacky exposed surface.